Fix conf_overwrite vlan/mgmt conflict

The pattern /^vlan\s+\d{1,4}\b/ matched both VLAN membership entries
(vlan N <ports>) and management entries (vlan N mgmt), causing them
to overwrite each other in configuration[]. When saving, whichever
form came last in the cmd_log would dedupe the other out of the
final config — resulting in either lost membership or a stale mgmt
setting.

Split into two patterns using negative lookahead:
- /^vlan\s+\d{1,4}\s+mgmt$/      matches only mgmt entries
- /^vlan\s+\d{1,4}(?!\s+mgmt\b)/  matches everything else

Both dedup independently. Discovered via hardware test on 6XH-X
where 'vlan 44 mgmt' silently dropped 'vlan 44 management 2t 5u'
from saved config, locking out web UI on next boot.

html/config.js

@@ -32,7 +32,8 @@ const conf_overwrite = [
   /^syslog\s+ip\b/,
   /^syslog\b/,
   /^passwd\b/,
-  /^vlan\s+\d{1,4}\b/,
+  /^vlan\s+\d{1,4}\s+mgmt$/,
+  /^vlan\s+\d{1,4}(?!\s+mgmt\b)/,
   /^pvid\s+\d{1,2}\b/,
   /^ingress\b/,
   /^port\s+\d{1,2}\s+name\b/,